This application claims the benefit of Korean Patent Application No. 2000-71353, filed in Korea on Nov. 28, 2000, which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device and more particularly, to a manufacturing process of liquid crystal cells for small sized liquid crystal display devices.
2. Discussion of the Related Art
A conventional liquid crystal display (LCD) panel has upper and lower substrates and a liquid crystal layer interposed therebetween. The upper substrate includes common electrodes, and the lower substrate includes switching elements, such as thin film transistors (TFTs), and pixel electrodes. The common electrodes and pixel electrodes are formed on upper and lower substrates, respectively, and a seal is formed on the lower substrate. The upper and lower substrates are then bonded together using a sealing material so that the common electrodes of the upper substrate and the pixel electrodes of the lower substrate come face to face with each other. A liquid crystal material is injected through injection holes of the seal into a gap formed between the upper and lower substrates through injection holes, and the injection holes are sealed. Polarizing films are attached to outer surfaces of the upper and lower substrates.
During operation of the liquid crystal panel, light passing through the liquid crystal panel is controlled by electric fields. The electric fields are applied by the pixel and common electrodes. By controlling the electric fields, image data (characters) are displayed on the liquid crystal panel.
Fabrication processes of various components of the liquid crystal display device, such as the thin film transistors and color filters, conventionally require numerous manufacturing steps. FIG. 1 is a flow chart illustrating a fabricating sequence of the liquid crystal cell for a conventional liquid crystal display device.
In FIG. 1, a first step ST1 involves cleaning the upper and lower substrates, commonly referred to as a color filter substrate and an array substrate, respectively. The first step ST1 removes impurities that may exist on the substrates and on one or more of the cells that have been previously formed on the upper and lower substrates.
In FIG. 1, a second step ST2 involves formation of alignment layers on the common and pixel electrodes previously formed on the upper and lower substrates, respectively. The second step ST2 also includes processes for coating, hardening, and rubbing of the alignment layers. A polyimide-based resin is conventionally selected for forming the alignment layers because it demonstrates excellent alignment characteristics with various liquid crystal materials. A surface of the hardened alignment layers is rubbed by a fabric to create surface scratches along a uniform direction. The rubbing process is necessary to form uniform alignment of the liquid crystal molecules in the liquid crystal layer, thereby ensuring uniform display. Accordingly, it is very important to uniformly form the alignment layers on a large surface of the common and pixel electrodes.
In FIG. 1, a third step ST3 involves printing a seal pattern and spacers on one, or both of the substrates. When the upper and lower substrates are attached, the seal pattern forms cell gaps between the upper and lower substrates that will receive the liquid crystal material. The seal pattern prevents the liquid crystal material from escaping out of the completed liquid crystal cell. A thermosetting resin that includes glass fibers, and a screen-print process are conventionally used to fabricate the seal pattern. The seal pattern includes an injection hole, and is formed along edge portions of a display area of each liquid crystal cell. After the seal pattern is printed, spacers are formed to maintain an accurate and uniform cell gap between the upper and lower substrates. Accordingly, the spacers must be formed on one, or both of the substrates with a uniform density. Presently, there are two processes for forming the spacers. A first process includes a wet dispensing method for spraying a mixture of alcohol and the spacers. A second process includes a dry dispensing method for spraying only the spacers.
In FIG. 1, a fourth step ST4 involves aligning and attaching the upper and lower substrates to each other. Accordingly, an aligning error margin in the fourth step ST4 is less than a few micrometers. If the upper and lower substrates are aligned and attached with an aligning margin larger than the aligning error margin less than a few micrometers, display quality of the display panel deteriorates due to leakage of light during operation of the liquid crystal cell.
In FIG. 1, a fifth step ST5 involves cutting the liquid crystal cell fabricated in the steps ST1-ST4 into individual liquid crystal cells. The cutting process includes a step of scribing the substrates to form cutting lines, and a step of severing the substrates along the scribed lines to form the individual liquid crystal cells.
In FIG. 1, a sixth step ST6 involves injecting the liquid crystal material into the individual liquid crystal cells. Since each individual liquid crystal cell has a gap ratio of only a few micrometers per hundreds of square centimeters in substrate surface area, a vacuum injection process utilizing a pressure difference is conventionally used for the liquid crystal cell. Since the vacuum injection process requires a significant amount of time in addition to the many other different fabrication processes for forming the liquid crystal display device, it is important to set an optimum condition for the vacuum injection process to increase fabrication yield. However, since there is no pressure difference between an interior of the liquid crystal cell and the liquid crystal material at the beginning of injection process, the liquid crystal material is injected by capillary action. When the liquid crystal material is injected into the liquid crystal cell, nitrogen gas or air is supplied to a vacuum chamber, thereby creating a pressure difference between the interior of the liquid crystal cell and an interior of the vacuum chamber. Accordingly, the liquid crystal material is injected into the liquid crystal cell as a result of the pressure difference. After the liquid crystal material is injected into the liquid crystal cell through an injection hole, the injection hole is sealed. The injection hole is conventionally sealed by forming an ultraviolet curable resin plug in the injection hole using a dispenser, and irradiating the plug with ultraviolet light to cure the resin and seal the hole. However, since the liquid crystal cell may become contaminated when exposed to air, the unsealed liquid crystal cell must be protected from the air and must not be allowed to be exposed to the air for a long period of time.
In FIG. 1, a seventh step ST7 involves inspecting the liquid crystal cell. A plurality of data lines and a plurality of gate lines of a unit cell are connected to a data pad and a gate pad, respectively, via shorting bars disposed in a marginal space of the liquid crystal cell. The marginal space includes a common voltage pad for applying a common voltage to the common electrode of the unit cell. The inspection is conducted by applying a voltage to the liquid crystal cell and observing an image displayed on the liquid crystal cell with a naked eye or with a microscope. In the inspection process, various qualities may be inspected. An existence of contaminates in the liquid crystal cell, point defects caused by the thin film transistors, line defects caused by discontinuities of the gate and data lines, and a optical defect properties caused by a differences of cell thickness, for example, may be inspected. Two inspection methods may be performed that include an ON-OFF inspection process, and an auto probe inspection process. The ON-OFF inspection process is performed by applying a direct current voltage using an ON-OFF apparatus and the auto probe inspection process is performed by applying an alternating current voltage using an auto probe apparatus.
In FIG. 1, an eighth step ST8 involves a grinding process. Static electricity that may have accumulated during the previous process steps is removed during the grinding process, and the shorting bars are cut away. Additional liquid crystal module processes may follow the grinding process.
FIG. 2 is a view showing an example of the ON-OFF inspection process of the liquid crystal cell for conventional small sized liquid crystal display devices. In general, the liquid crystal cell for small sized liquid crystal display devices is manufactured according to the processes of FIG. 1. In FIG. 2, a unit cell 10 is loaded onto the ON-OFF apparatus 20, which is sized for the unit cell 10. A plurality of pads 14 for inspection are formed in a marginal space of the unit cell 10. A voltage is applied to the unit cell 10 through the pads 14, thereby displaying an image, and an inspection process is performed. However, the ON-OFF inspection process based on a unit cell is problematic. First, when a 370 mmxc3x97470 mm glass substrate is used, a total of about 64 50 mmxc3x9750 mm unit cells can be obtained. If each of the 64 unit cells are individually inspected on the ON-OFF apparatus, a significant amount of time is required due to handling of the small sized unit cell. Furthermore, since each of the unit cells needs to be inspected individually, Turn Around Time (TAT) for each unit cell is increased, thereby decreasing resulting in low productivity.
Accordingly, the present invention is directed to a manufacturing method of liquid crystal cells for small sized liquid crystal display devices that substantially obviates one or more of problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide an inspection method of liquid crystal cells for small sized liquid crystal display devices for reducing inspection process time.
Another object of the present invention is to provide an inspection method of liquid crystal cells for small sized liquid crystal display devices to improve handling of the liquid crystal cells.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a manufacturing method of liquid crystal cells for a liquid crystal display device includes forming a first plurality of liquid crystal cells that include a color filter and a common electrode on an upper substrate, forming a second plurality of liquid crystal cells that include a plurality of gate lines and a plurality of data lines on a lower substrate, forming a gate contact pad in a marginal space of the lower substrate, the gate pad connected to a first group of the plurality of gate lines of one of a common row and common column of the second plurality of cells, forming a data contact pad in the marginal space of the lower substrate, the data pad connected to a first group of the plurality of data lines of one of a common row and common column of the second plurality of cells, forming a common voltage contact pad on the lower substrate for applying a common voltage to the common electrode on the upper substrate, forming an assembled substrate by bonding the lower substrate to the upper substrate, separating the assembled substrate into sub-substrates that include at least the second plurality of liquid crystal cells arranged in the one of a common row and common column, introducing liquid crystal material into the liquid crystal cells of the sub-substrate, and inspecting the liquid crystal cells of the sub-substrate by applying a voltage to the gate contact pad, the data contact pad and the common voltage contact pad.
In another aspect, a liquid crystal display device includes upper and lower substrates, a first plurality of liquid crystal cells including a color filter and a common electrode on the upper substrate, a second plurality of liquid crystal cells including a plurality of gate lines and a plurality of data lines on the lower substrate, a gate contact pad in a marginal space of the lower substrate, the gate pad connected to a first group of the plurality of gate lines of one of a common row and common column of the second plurality of cells, a data contact pad in the marginal space of the lower substrate, the data pad connected to a first group of the plurality of data lines of one of a common row and common column of the second plurality of cells, and a common voltage contact pad on the lower substrate for applying a common voltage to the common electrode on the upper substrate.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.